Gate-tunable synthetic antiferromagnetism with nonrelativistic spin splitting in a graphene/MnS/graphene heterostructure

Abstract

We propose encapsulating type-A antiferromagnetic semiconductors between graphene layers to realize a gate-tunable synthetic antiferromagnet with nonrelativistic spin splitting, enabling efficient spintronic transport via graphene. Ab initio calculations and tight-binding models of graphene/MnS/graphene heterostructure reveal that gate-tuning of the heterostructure breaks top/bottom graphene equivalence, inducing opposite ferromagnetic proximity exchange that lifts spin degeneracy to yield nonrelativistic spin splitting at the Fermi level, dominating over relativistic effects. The induced effects manifest as conductance dips in spin-resolved transport through proximitized graphene nanoribbons, observable as giant magnetoresistance within a narrow energy window around the Fermi level. Our graphene/type-A antiferromagnetic heterostructure, a readily synthesizable platform incorporating antiferromagnets with nonrelativistic spin splitting, pave the way for gate-manipulated, low-dimensional antiferromagnetic devices.

Figures (3)

• Figure 1: Schematic view of the transport device which implements the synthetic vdW NRSS AFM formed by encapsulating monolayer MnS (type-A AFM semiconductor) between graphene layers. The source and drain are labeled with S and D, respectively, connecting the top and bottom graphene. The central region consists of graphene/MnS/graphene under applied perpendicular electric field $E$ modulated by a gate voltage.
• Figure 2: Calculated band structure of graphene/MnS/graphene heterostructure under an applied out-of-plane electric field of $E=\pm 1$ V/nm (relativistic case), plotted along the high symmetry points MK$\Gamma$ in graphene Brillouin zone. The plot shows a narrow energy window of $[-30,\,30]$ meV around the Fermi level, in which the bands are confined to the (proximitized) graphene layers. The color scale indicates the expectation value of the spin $z$-component, revealing nearly perfect $\pm 1/2$ spin polarization along $z$. Black circles (squares) denote projections onto top (bottom) graphene orbitals, highlighting the electric-field-tunable shift of the Dirac cones in the top (bottom) layer.
• Figure 3: Conductance as a function of energy $\varepsilon$ for graphene nanoribbon of length 48 $\text{\normalfont\AA}$ and width of 17.8 $\text{\normalfont\AA}$ at electric field strength $E=-1$ V/nm. Two local minima appear at positive/negative energies, corresponding to signals from the bottom/top graphene layers.